1. Field of the Invention
The present invention relates to a battery pack and a remaining battery power calculation method, and more particularly, to a battery pack and a remaining battery power calculation method capable of calculating remaining battery power according to the temperature of the battery pack during use.
2. Related Art
Battery packs (secondary batteries) such as liquid ion batteries have specific capacities, and their capacities have the characteristic of varying according to the temperature under which the battery pack is used.
When a battery pack is used under low temperature, the internal impedance of its battery cell increases and when the same current as normal temperature is applied, a large voltage drop occurs, so that the capacity of the battery pack decreases.
FIG. 6 is a graph showing discharge characteristics of a battery pack at 25° C., 10° C. and 0° C. The abscissa represents time, while the ordinate represents voltage.
As shown in FIG. 6, in the case of discharge of 2.0 W and end voltage of 3.35 V, the following measurement result is obtained: if a dischargeable capacity in an environment of 25° C. is set to 100%, for example, the measurement shows approximately 80% dischargeable capacity under an environment of 10° C. and approximately 60% dischargeable capacity under an environment of 0° C.
The technique of detecting the temperature of a battery pack by using a temperature sensor and correcting the remaining battery power has heretofore been used to correct battery capacity diminutions during use at low temperatures, like described in Japanese Laid-Open Patent Application JP-A-2000-260488 (Paragraph Numbers [0038]-[0072]).
In this case, the current thermistor temperature is measured to correct a usable time in the current temperature environment. Accordingly, in environments of lower temperature, displayed usable time tends to become shorter.